Hydroalium alloy for die-casting use



INVENTORS.

ATTO RN EY Filed 001'.. l. 1965 Oct'- 18,1966 sHolcHl FUJlsAwA E-rAL n HYDROALIUM ALLOY FOR DIE-CASTING USE United States Patent O 3,279,915 HYDROALIUM ALLOY FOR DIE-CAS FING USE Shoichi Fujisawa, Kenji Hayam, Takao Nihashi, and Kenichi Yokoi, all of Hamamatsu-sh, Shizuoka-ken, Japan, assignors to Honda Giken Kogyo Kabushik Kasha, Tokyo, Japan, a corporation of Japan Filed oct. 1, 1963, ser. No. 312,914 Claims priority, application Japan, Oct. 15, 1962, 37/44,711 2 Claims. (Cl. 75-147) This invention relates to hydroalium or aluminummagnesium alloys for die-casting use.

Hydroalium alloys are generally characterized by their high corrosion resistance and castings of the alloy can semiperrnanently maintain their glittering metallic luster, even in a moist atmosphere, if the cast surfaces are merely buied. The -conventional alloys, however, involve a number of drawbacks including poor uidity and a resulting high rejection rate when utilized in a casting operation. Particularly in the die-casting of these alloys, the removal of the casting from the mold cavity involves some difficulty and the service life of the metal mold is very limited. In some instances, the casting even lacks the feature of high corrosion resistance even though the alloys are inherently corrosion-resistant. Under these circumstances, common practice has been to minimize the amounts of Mn, Fe, Cu, Zn, Sn, Ni, Cr, etc. contained as impurities in this type of alloy in order to increase its corrosion resistance. Also, it has generally been supposed that, the higher the Si content, the higher the fluidity of the alloy during the casting process, but that any Si content exceeding greatly reduces the mechanical strength of the cast product.

Intensive research conducted by the inventor has revealed the fact that the impurity contents of the hydroalium alloy should not be limited as before but rather be increased to increase the fluidity of the alloy since the cast surface usually includes many features defined by sharp corners and edges. If the fluidity of the melt is limited the sharp corners and edges are not properly filled and this largely promotes corrosion of the casting. Moreover, it has been found that the effects of the above impurities upon the hydroalium alloy when die-cast are quite different from those when cast conventionally in a sand or metal mold. Furthermore, it has been found that inclusion of Fe and Mn as effective or useful ingredients but not as impurities as specified in the Japanese Industrial Stan-dard and corresponding foreign standards improves the die-casting properties of the alloy without adversely affecting its corrosion resist-ance particularly when Fe (molecular weight approximately 56) and Mn (molecular weight approximately 55) are present substantially in equal molar amounts and that inclusion of Si as a useful ingredient in addition to the inclusion of Fe and Mn highly improves the die-casting properties of the alloy without detracting from its mechanical strength as long as the Si content is of the order of 3.0% or less by weight.

Upon the lbasis of the above, the present invention provides an aluminum base die-casting alloy of the following composition:

Percent by weight Mg 2.0 to 12.0 Si 0.5 to 3.0 Fe 0.8 to 1.2 Mn 0.6 to 1.2 Sn 0.1 Cu 0.2 Ni 0.1 Zn 0.1

Ti 0.l

ACC

Percent by weight Pb 0.1 Cr 02 A1 rest Fe, Mn Iare present in substantially equal molar or equimolar amounts.

In the accompanying drawing,

FIG. 1 is a micrograph X100 illustrating the die-cast structure of the casting alloy in accordance with the intion; and

FIG. 2 is a microgr-aph of the same magnification illustrating the structure of a conventional alloy as cast in a metal mold.

The effects of the alloying elements on the properties of the hydroalium alloy will be apparent from the following description and from a comparison between FIGS. 1 and 2.

According to the prior art, Si contained in the alloy improves the casting properties of the alloy in conventional s'and or metal-mold casting processes but in cases where the Si content exceeds 0.1% it causes the formation of MgzSi, a brittle intermetallic compound, which does not impair the corrosion resistance but greatly red-uces the mechanical strength of the casting and particularly its impact strength. In die-casting, however, Si does not reduce the mechanical strength of the cast product but further improves the casting properties of the alloy even if the Si content reaches 3.0%. Such improvement in casting properties makes it possible to obtain castings having smoother surfaces and a higher corrosion resistance. The reason why Si does not reduce the mechanical strength has been made clear from observations of the characteristic properties of the die-cast product. In die-casting, it is supposed that the molten metal is injected in mist form through the gate by means of a highpressure plunger into the cavity of the metal mold and is cooled to solidity therein unde-r pressure and in an instantaneous manner. This is the reason why the comparatively high Si content does not allow any substantial formation of the intermetallic compound, MggSi during die-casting.

Next, the effects of Fe and Mn will be described. As previously stated, the alloy embodying the invention contains Fe and Mn as useful ingredients in relatively large amounts. During the die-casting process, the relatively high Fe and Mn contents prevent formation of any solid solution between the metal mold and the alloy and hence prevent any adhesion of the alloy casting to the metal mold, facilitating the removal of the casting therefrom. In case Fe or Mn alone is contained in the casting alloy, it forms an intermetallic compound, FeAl3 or MnAls, which acts to promote corrosion of the casting due to the large potential dilference between the compound and Al. However, according to the present invention, Fe and Mn are contained in equal molar amounts and together form an intermetallic compound of (FeMn)Al6. The limited potential diierence between this intermetallic compound and Al accounts for the fact that the adverse effects of the high Fe and Mn contents have not any substantial influence upon the corrosion resistance of the alloy. However, it is desirable to limit each of the Fe and Mn contents each to a range of from 0.6 to 1.2% as any excessive Fe or Mn content reduces the corrosion resistance of the alloy, as indicated above. This range is desirable also for preventing formation of any solid solution between the injected metal and the mold.

Such elements as Sn, Cu, Ni, Zn, and Cr are detrimental to the corrosion resistance of the alloy and should be eliminated as far as possible as in the case of conventional hydroalium alloys.

Some examples of the composition of the aluminum base alloy follow:

For comparison, the composition of a conventional hydroalium alloy is illustrated below (IIS, AC7A: virgin hydro Mgr-Al).

Composition Cu Si Mg Fe Mn Al C 5.27 0.14 0.25 rest.

A large number of test pieces were prepared from diecastings of the three compositions and tested for their strength under bending stresses. The pieces of composition A exhibited an increase in strength of approximately 25% relative to those conventional composition C while the pieces of composition B exhibited an increase -of approximately 13%. Also, the pieces of composition A as well as of composition B were iinally ruptured whereas those of composition C were only flexed.

It is apparent from the above that die-castings of the novel die-casting alloy have an improved strength compared With conventional hydroalium die-casting alloys and that die-castings of compositions A or B are harder and therefore have an improved machinability.

In addition, it has been observed that both compositions A and B including Fe and Mn in equal molar amounts, give a corrosion resistance at least comparable to that obtained with composition C despite the rfact that compositions A and B each include high Fe and Mn contents. Further, in the casting operation, the rejection rate of castings of composition A or B was approximately 12% whereas that of composition C was 30%.

The alloy of the present invention, which contains Fe, Mn and Si in large amounts, exhibits improved casting properties as compared with conventional hydroalium alloys since it never adheres to the metal mold during the die-casting process and hence prolongs the service life of the metal mold. This advantageous feature of the novel alloy enables an increased production rate, i.e. an increased number of die-casting shots per unit time. In the experimental production of a test object, only 143 pieces per hour could be die-cast from the conventional alloy of composition C, but the rate of 200 or more pieces per hour was possible with the alloys of compositions A and B.

In addition to these yimportant practical advantages, the use of the rnovel alloy for die-casting purposes has a further economic advantage in that relatively inexpensive raW materials can be used as basic ingredients for production of the alloy due to its high permissible impurity content.

What is claimed is:

1. An aluminum base alloy for die-casting consisting essentially of: 2.0 to 12.0% by weight of magnesium; 0.5 to 3.0% jby weight of silicon; 0.6 to 1.2% by weight of iron; and 0.6 to 1.2% by Weight of manganese, the balance consisting essentially of aluminum, said iron and said manganese being present in substantially equimolar amounts.

2. The alloy according to claim 1, further comprising the following elements in less than the respective maximum amounts indicated in percent by weight:

References Cited by the Examiner UNITED STATES PATENTS 12/1938 Spitaler 75-147 1/1940 Spitaler 75-147 6/1952 Fritzlen 75-147 FOREIGN PATENTS 1 l/ 1942 Sweden.

DAVID L. RECK, Primary Examiner.

C. N. LOVELL, Assistant Examiner. 

1. AN AN ALUMINUM BASE ALLOY FOR DIE-CASTING CONSISTING ESSENTIALLY OF: 2.0 TO 12.0% BY WEIGHT OF MAGNESIUM; 0.5 TO 3.0% BY WEIGHT OF SILICON; 0.6 TO 1.2% BY WEIGHT OF IRON; AND 0.6 TO 1.2% BY WEIGHT OF MANGANESE, THE BALANCE CONSISTING ESSENTIALLY OF ALUMINUM, SAID IRON AND SAID MANGANESE BEING PERSENT IN SUBSTANTIALLY EQUIMOLAR AMOUNTS. 